The present invention relates to a vehicle such as a farm vehicle, and particularly, to a vehicle having a front wheel assembly that adjusts the spacing between the front wheels, for example, to match the row spacing of a crop. More particularly, the present invention relates to a steering mechanism that turns the front wheels of the vehicle when the front wheels are at any position between maximum and minimum spacings.
Farm vehicles having front wheels that can be moved to adjust the spacing between the wheels are known in the art. See, for example, U.S. Pat. No. 5,489,113 to Torborg; U.S. Pat. No. 5,282,644 to Larson; and U.S. Pat. No. 4,350,222 to Lutteke et al., each of which disclose mechanisms for adjusting the spacing between front wheels of a vehicle. It is desirable to adjust the spacing between front wheels of the farm vehicle to match the row spacing of a crop in which the vehicle is being used to minimize damage to the crop.
Some farm vehicles having front wheel adjustment mechanisms include separate hydraulic cylinders that are actuated to turn the front wheels of the vehicle thereby providing for steering of the vehicle. See, for example, the '113 patent to Torborg; the '644 patent to Larson; and U.S. Pat. No. 5,039,129 to Balmer and U.S. Pat. No. 3,782,491 to Herbenar, each of which disclose hydraulic cylinders having pistons that are linearly extended and retracted to turn the front wheels of a farm vehicle.
Many vehicles include tie rods that couple front wheels of the vehicle together so that the front wheels turn in unison during steering of the vehicle. Many conventional tie rods move toward one side of the vehicle or the other as the front wheels are turned. Some vehicles that include front wheel adjustment mechanisms also include tie rods that are adjusted as the spacing between the front wheels is adjusted. In such vehicles, a mechanism is usually provided for fixing the length of the tie rod after adjustment. See, for example, the Herbenar '491 patent which shows a tie rod including telescoping rods having a pin which can be manually inserted through one set of a series of bores formed in the rods to rigidly couple the rods together after the length has been adjusted. Also see the Torborg '113 patent, which shows a tie rod including a linear hydraulic cylinder that is actuated by a complex hydraulic system to adjust the length of the tie rod as the spacing between the front wheels of the vehicle is hydraulically adjusted.
In practice, many adjustable tie rod systems can cause variations of the toe-in angle of the front wheels as the distance between the front wheels is adjusted. For example, tie rods of the type disclosed in the Herbenar '491 patent can be indexed only by discrete distances dictated by the spacing between the bores formed in the rods. Hydraulic tie rods of the type disclosed in the Torborg '113 patent can experience internal hydraulic fluid loss between moving mechanical components and external hydraulic fluid loss due to leakage. The hydraulic fluid losses of one hydraulic cylinder are inherently different from the hydraulic fluid losses of another hydraulic cylinder. Thus, with regard to a wheel spacing and tie rod system of the type disclosed in the Torborg '113 patent, the hydraulic tie rod cylinder and the hydraulic cylinders that change the wheel spacing must be rephased after several front wheel spacing adjustments to prevent toe-in angle variations from occuring during wheel spacing adjustments.
What is needed is a vehicle having a wheel-spacing mechanism for adjusting the distance between front wheels of the vehicle and a steering system including a mechanism that ties the front wheels together so that the front wheels turn in unison, but that does not result in toe-in angle variations as the spacing between the front wheels is adjusted. Vehicle operators would welcome a vehicle having a steering system that automatically adjusts when the front wheel spacing is adjusted without the need to separately manipulate any part of the steering system and without the need to rephase the steering system after repeated front wheel adjustments.
According to the present invention, a vehicle is provided with a wheel-spacing mechanism including a center axle tube and an axle arm extending from each end of the center axle tube. L-shaped spindles are coupled to each axle arm for pivoting movement about a substantially vertical axis and front wheels are mounted to respective spindle shafts for rotation about a substantially horizontal axis. A hydraulic cylinder connects each axle arm to the center axle tube so that extension and retraction of the hydraulic cylinders telescopically moves the axle arms relative to the center axle tube thereby adjusting the distance between the front wheels.
The vehicle is also provided with a steering mechanism including a central rotary hydraulic motor mounted on the center axle tube and a pair of telescoping drive shafts extending outwardly away from the hydraulic motor in opposite directions. Each telescoping drive shaft includes an inner shaft that couples to the rotary motor for rotation about a generally horizontal drive axis and an outer shaft that couples to the inner shaft for telescoping movement relative to the inner shaft along the horizontal drive axis. Extension and retraction of the hydraulic cylinders connecting the center axle tube to the axle arms automatically causes the outer shafts to telescope relative to the inner shafts.
The vehicle includes a steering wheel operably coupled to the rotary hydraulic motor through a hydraulic control system so that rotation of the steering wheel operates the rotary hydraulic motor. Operation of the rotary hydraulic motor results in rotation of both inner shafts about the common horizontal drive axis. In addition, each inner shaft is rotationally drivingly coupled to the respective outer shaft so that rotation of the inner shafts by the hydraulic motor results in rotation of the outer shafts.
The steering mechanism of the present invention includes a pair of gear boxes, each of which includes an input shaft that couples to the respective outer shaft of the telescoping drive shafts to rotate therewith about the horizontal drive axis in response to rotation of the steering wheel. Each gear box is also coupled to a respective L-shaped spindle shaft so that rotation of the outer shafts about the horizontal drive axis results in pivoting movement of the spindle shafts about their respective vertical axes, thereby causing the front wheels of the farm vehicle to turn in unison.
Additional objects, features, and advantages of the invention will become apparent to those skilled in the art upon consideration of the following detailed description of a preferred embodiment exemplifying the best mode of carrying out the invention as presently perceived.